Variable pitch airscrew



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I HTTQRNEYJZ Feb.. i5, E949. R. H. WARE I zamgg 4 VARIABLE FITCH AmsonnwFiled Aug. 2, 194s 's sheets-sheet 2 .H TTRJVEYS.

Patented Feb. Vl5, 194.9

VARIABLE PITCH AIRSCREW Robert Henry Warde, Hatfield, England, asslgnorto The De Havilland Aircraft Company Limited, Hatfield, EnglandApplication August 2, 1943, Serial No. 497,082 In Great Britain May 8,1942 This invention relates to a variable pitch propeller incorporatinga double-actingv hydraulically-operated ram, reciprocation of whichisf..

translated by suitable mechanism into rotation of the propeller bladeseach about its pitchchange axis. More particularly the invention isconcerned with propellers in which the supply of hydraulic fluid to theram is controlled by a governor-operated valve, which by movement underchanging speed conditions directs the hydraulic pressure fluid throughsuitable porting selectively either to the inboard end or outboard endof` the ram, the direction of pitch-change thus being determined by thedirection of movement of the valve. For convenience in description andin the claims, such a propeller is hereinafter designated a variablepitch propeller of the kind hereinbefore specied.

In such variable pitchl propeller ofthe kind hereinbefore specified ithas previously been proposed to arrange the porting associated with thegovernor-controlled valve so that when the engine speed falls below apredetermined value the valve moves to permit flow of hydraulic fluid(usually engine oil) to the outboard end of the ram to move it rearwards(assuming a tractor airscrew),the inboard end of the ram being at thesame time connected to drain (usually the engine sump). The resultantoperation of the ram moves the blades towards fine pitch, and thereduction in blade angle reduces load and tends to increase the enginespeed. Conversely, increase in engine speed causes the governor to movethe valve in the opposite sense from that just described, allowinghydraulic fluid from a pump to pass to the inboard end of the ram, 'thusmoving it against the lower engine oil pressure acting on the outboardend of the ram. For feathering and unfeathering operations, hydraulicfluid from a high-pressure pump is applied to the ram independently ofthe porting associated with the control valve, the direction ofpitch-change being' determined by a reversing valve in the airscrew.

In another construction it has been proposed to arrange the portingassociated with the governor-controled valve so that when the engineover-speeds the governor-controlled valve moves so that one end of thepitch-change ram is connected to the hydraulic iluid supply from thepressure side of a pump; whereas the other end l I 15 claims. (c1.17o-460.2)

' of the ram is connected to the suction side of the pump. In such anarrangement, for feathering and unfeathering operations thegovernorcontrolled valve is manually operable so as to ensure thehydraulic iluid being directed at will either to the inboard or outboardend of the ram, as required, to move the blades towards coarse or finepitch.

According to the present invention it is proposed in a variable pitchpropeller of the kind hereinbefore specifled to arrange thegovernoroperated valve and its associated porting so that for anunder-speed condition the outboard end of the ram is connected. to lowpressure actuating fluid supply (usually engine oil), and the inboardend of the ram is connected to drain; Whereas, conversely, in theover-speed condition the outboard end of the rain is connected to drainwhile the inboard end is supplied with actuating fluid at intermediatepressure from av boost pump. Furthermore, in a preferred arrangement ahighpressure pump is provided to supply hydraulic fluid at highpressure'for feathering -and unfeathering operations, the arrangementbeing such that operation lof the high-pressure fluid circuit controlscut-olf valves in the normal pitch-change actuating fluid circuit toclose off the normal actuating uid circuit and permit high-pressurefluid-flow to the ram through the porting associated with thegovernor-operated valve to the outboard or inboard end of the ram,

according to the position of the governor-operated valve, which forfeathering and unfeathering operations is manually operated. It shouldbe understood that while for convenience of description the wordsinboard and outboard have been used in a particular relation to thepressure system described, it is within the scope of the invention tohave pressure on the outboard end of the ram, causing pitch-changetowards coarse pitch. Moreover, high or low pressure may be used oneither side of the ram.

It will be realised that the arrangement according to the presentinvention avoids the neces sity for a reversing valve in the airscrew.Likewise, instead of high-pressure fluid being required for pitch-changetowards both fine and coarse pitch positions, the arrangement accordingto the cording to the present invention; for purposes of il'ustrationand with connectingl conduits indicated in chain lines. theassociated-airscrew is shown very diagrammatically and to a very muchreduced scale;

Figure 2 is an inverted plan view looking in the direction of the arrowX on Figurel;

Figure 3 is a side elevation partly sectioned looking in the directionof the arrow .Y on Figure 1;

Figure 4 is a section taken looking downwardly at the line IV--IV onFigure 3; while Figure 5 is a section takenl looking rightwardly on theline V-V on Figure 1.

lReferring now to the drawings, the body of the governor-operated valveis represented by the reference numeral 6. A ported sleeve 1 is locatedin a suitable drilling in the body 6 and is driven for rotation by thesplined coupling 8, or equivalent driving member, from a suitablecountershaft drive 01T the engine. The sleeve 'l defines with thedrilling in which it is iltted the four annuli 9, I0, II and I2, ofwhich the annulus 9 leads to the inboard end I3 of the pitch-change ramI4 through the connection I1; whereas the annulus I2 leads to theoutboard end i5 of the ram through the connection I5. Of the annuli I0and II, Ill is supplied with boosted pressure with the governor-operatedvalve spindle i9, the

lower end whereof is hollow and open to drain by way of sleeve 1, andwhich incorporates the four lands 20, 2|, 22 and 23, and also the drain.port 24 between the lands 20 and 2i. It should be noted that its lowerend, below the land 23, is in effect a further drain valve, when raisedto clear the'annulus I2. At operation in overspeed conditions, thegovernor-weights I8 are caused to swing out about their pivots and raisethe governor-operated valve spindle I9 against the loading exerted bythe spring 25; whereas for underspeed conditions the spring 25 is ableto overcome the centrifugal loading exerted by the governor-Weights I8to move the spindle I9 downwardly.

The lands 20, 2|, 22 and 23 are so spaced with respect to theco-operating annuli 9, I0, II and I2 that in the position shown inFigure 1, corresponding to constant speeding position for normaloperation, all the annuli can be blanked-off from inter-communication.If, however, the engine speeds up, an overspeed condition occurs and thevalve spindle I9 is raised, boosted engine o il from the annulus I0being then free to flow to the annulus 9 between the lands 2I and `22(then raised slightly from the Figure 1 position), and to the inboardend of the ram to coarsen the blade pitch and reduce engine speedappropriately by increasing the loading on the engine. Such raising ofthe valve I9 also takes the land 23 clear of the annulus I2, so that inoperation of the ram I4 for coarsening pitch, oil is permitted to flowto drain through the connection I6 and sleeve 1 past the raised land2,3. Conversely, an underspeed condition resulting in lowering of thevalve spindle I9 establishes communication between the engine oilannulus II and the annulus I2 connected to the outboard en'd I5 01E- thepitchchange ram to move the blades towards fine pitch and so relievingthe load on the engine to permit it to speed up. Such downward movementof the valve spindle I9 puts the annulus, 8, leading by way ofconnection I1 from the inboard end of the ram, into communication withdrain through the port 24 between the lands 20 and 2i of thegovernor-operated valve spindle I9.

In regard to the delivery of oil to the annuli I0 and II for constantspeeding operation of the airscrew, oil is fed from the engine to theconstant speed unit booster gear pump inlet 26. The gear pump rotors areseen in Figure 1 at 21 and 28.

lThe outlet from the gear pump in the arrangement shown is acontinuation of the port blankedofi by the screw plug 29; see Figure 2.It will be observed that at the gear pump inlet there is a through port3l so that the engine oil-flow is in fact sub-divided. A part goes toand through the booster pump, eventually to the port 41 and annulus I0,and another part by-pastes the pump by way of port 3|, eventually to theport 45 and annulus I I. Thus, oil at pressure supplied by the engineoil pump flows up the through port 3i of the gear pump rotor, throughthe port 32 into the feathering valve housing sleeve 33; The featheringvalve housing sleeve 33 has the three annular grooves 34, 35 and 36 fromwhich appropriate ports lead through into the bore of the sleeve, inwhich slides a featherlng valve 31, which itself has lands 38, 39 and40.

The feathering valve is hollow, being open at its end adjacent thefeathering oil inlet 4I, and having an outlet at its inner or closed endthrough the ports 42. Boosted engine oil from the gear pump rotors 21,28, flows into the back of the ieathering valve housing through theboosted engine oil port 43. The engine oil port 32 and the boostedengine oil port 43, and the general arbe understood that for normaloperations in the .45 ((see Figure 4).

constant speeding range the feathering valve 31 remains in the po-itionin which it is shown in Figure 4, so that the annulus 44 permits the owf of engine oil from the feathering valve sleeve annulus 35 to thefeathering valve sleeve annulus 34, from which latter engine oil canflow to the engine oil annulus II through the port On the other hand,the boosted engine oil entering the back of the feathering valve throughthe port 43 ows in through the inner end of the sleeve 33, through theports 46, into the feathering valve sleeve annulus 36 from which itflows through the port 41 to the governor-operated valve annulus I0.

It follows, therefore, that under normal constant speeding conditions(corresponding to positions of parts in Figures 1 and 4) oil at thenormal pressure supplied by the engine oil pump is always incommunication with the engine oil annulus II; whereas oil boosted by thegear pump above engine oil pressure is always available at the boostedengine oil annulus I0. While, therefore, if the engine is operating at aselected rconstant speed the governor-operated valve spindle I9 reyasomar mains in the position shown in Figure v1., if on the other handthere is a departure from the selected Yconstant speed, thegovernor-operated valve concerned, namely: ordinary engineoil suppliedby the engine oil pump, and the boosted engine oil discharged from .thegear pump rotors 21 and 28 built into the constant speed unit. ForAfeathering and unfeathering operations, however. oil is delivered pasta manual control valve by an auxiliary high-pressure` pump (neithershown herein) which supplies to the feathering control valve 31 throughthe feathering oil inlet 4I. The feathering oil pump is drivenindependently of the engine, preferably electrically, and whenfeathering oil flows to the feathering control valve 31, the valve 31 ispushed back against the loadingexertd -by the compression spring 48.

' When featheringloil is not supplied to the inlet 4l, compressionspring I9 loads the feathering cntrolvvalve'-r31 outwardly until theforward end oi' the feathering control valve 31 abuts the circlip orequivalent stop member B0, which thus denes the setting of thefeathering control valve 31 for normal constant speeding operation.

When the feathering control valve 31. is forced inwardly by the pressureagainst it of oil entering inlet passage II, the land I8 cuts off thesupply of engine oil from port 3B to the feather valve annulus 34 andannulus II of the governor-operated valve; while, similarly, the land 40at theI back end of the feathering control valve also cuts oil thesupply of boosted engine oil from the port 43 to feathering valveannulus 28 and annulus III of the governor-operated valve (see Figure 4)but feathering oil is then permitted to flow from the inlet 4I throughtheports 42 and 46j to the annulus 38.l from which it then flows by wayof port 41 to the governor-operated valve annulus I0.

2l, upon return of manual control spindle l2 to automatic controlposition. in which position of \the/governoroperated valve spindle Ilthe lands 22 and 22 serve to establish communication between the annuliII and I2. If the feathering oil high-pressure pump is then. operated,oil from it enters the inlet 4I. this'time for unfeathering, until suchtime as the land 2l has cleared the port leading in from the annulus Ilof the feathering valve sleeve. and feathering oil then flows along theport Il, through the annulus I I and the nowconnected annulus I2 andpipe Il to the outboard end of the ram. The feathering control valve 31is thus in the same position for unfeathering operations as itis forfeathering operations. but flow of oil from the feathering pump to theannulus II during the feathering operation is of l no consequencebecause with the governor-comtrolled valve spindle vIl raised manuallyfor the feathering operation the annulus I'I is blankedoff between thelands 22 and 22. Similarly, flow of high pressure oil to the annulus I0during unfeathering operation is immaterial, because with the spindle I0lowered for unfeathering the an- ;lilus I0 is blanked-off between thelands 2| and Figure illustrates a minor constructional detail providingfor adjustment of the down-limit position of the rack I3. for whichpurpose there is provided on the end of the spindle 52 the stop I5 theeventual limit pcsitln of which is dictated according to the position towhich the cooperating stop bolt I6 is adjusted. p

It is to be understood that the invention is ap.- plicable to alrscrewscapable of pitch change towards reverse pitch. and such an operationcould be in place of or in addition to feathering op- In the latter caseit will be desirable in the erations. to incorporate positive fine-pitchstops system.

WhatIclaim is:

1. In combination with a' hydro-controllable variable-pitch propellerhaving a pitch-changing ram operable through a normal range ofpitchwhich has so far been designated the "boosted enessary, namely. toadjust the governor-operated valve spindle manually, which operation isperformed by a manual'control lever remotely actuated by the pilot,usually coincidentally with admission oi' high pressure oil to the inletl I to turn the spindle 52 for operation of the rack-andpinionv gearingB3 and M (see Figures 1 and 3), which for feathering lifts thegovernor-operated valve spindle I8 to place the annulus III, thensupplied. with high-pressure oil. for feathering, in communication withthe annulus 9 leading to the inboard end of the pitch-change ram by-wayof the connection I1. a

I For an unfeathering operation the engine is invariably stopped so thatthev governor-operated increase and decrease, but within thatrangevbeing operable under the Influence of a low-pressure source onlyin the pitch-decreasing sense, and by a higher-pressure source only inthe pitch-increasing sense, and being further operablev through afeathering andunfeathering range of said propeller, beyond such normalrange o! .pitch-change, under the influence of a `still higher-pressuresource, a low-pressure fluid source and a higher-pressure iluid sourceappropriate to such operations, respectively, a casing having portsconnected, one to one 'end of the ram. another to the opposite end ofthe ram, and a third to drain, and for connection to said respectivepressure sources, valve means cooperating with said ports, governormeans operatively connected to said valve means lto effect movementthereof in one direction,

upon lowered speed to deliver low-pressure fluid to the pitch-decreasingend ot the' ram while connecting kthe opposite end oi' the ram to drain,and conversely, in the opposite direction, to deliver higher-pressurefluid to the pitch-increasing end of the ram for operation of the ram inpitch-increasing sense. while connecting the latters opposite end todrain. upon increased speed.

.2. Control means for a hydro-controllable vari.-

. able-pitch propeller such as has a pitch-changing ram operable througha normal range of pitch-change, but in the pitch-decreasing sense.

only. under the influencent low-pressure dinerential between alow-pressure fluid source and a f drain. as applied to the opposite endsoi said ram. and also operable through such normal range. but in thepitch-increasing sense, only, by a higher-pressure differential betweena higher pressure source and a drain, and further operablethrough afeathering range beyond such normal range oi' said propeller, under the'iniluence of a still higher-pressure diilerential between a sillhigherpressure fluid source and such drain, as.. applied similarly tothe opposite ends of said ram; .said control means comprising a casinghaving ports for connection, one to the pitch-increasing end of the ram,another to the pitch-decreasing end of such ram, and a third to drain,and having further ports for connection to the respective low, higher,and still higher-pressure sources, valve means cooperating with saidports, governor means operatively connected to said valve means to eiectmovement thereof in one direction upon lowered speed to deliver fluidfrom the low-pressure inlet port to that port which mis connected to thepitch-decreasing end of the ram, while connecting to drain that portwhich is connected to the opposite end of the ram; and conversely, inthe opposite direction, to deliver fluid from the higher-pressure inletport,to that port which` is connected to the pitch-increasing end oi'`the ram, while connecting to drain that port which is connected to theopposite end oi' the ram, upon increased speed. Y

3. The combination of claim 1, including a. booster pump receiving oilfrom the engine and supplying it t the appropriate casing port Iorhigher pressur operation.

-4. The combination of claim l; including a feathering valve interposedbetween the low pressure and higher pressure sources and thegovernor-controlled valve and its ports, said feathering valve beingoperable to maintain communication normally between said sources and thegovernor-controlled valve, but to cut suchconn still higher highpressure oil to said feathering valve to shift it, and thus to esablishcommunication between such still higher high pressure supply and thegovernor-controlled valve and its ports, and means operable at will toshift the governor-controlled valve to admit the still higher pressureoil by way of the governor-controlled valve to the ram, for operationoi' the variablepitch propeller within the feathering range.

5. The combination of claim 2, wherein the still higher pressurefluidsource is arranged operatively for connection to the ram to operate thelatter within the feathering Yrange of said propeller, the control meansfurthercomprising a featheringvalve disposed in operative connectionwith the low-pressure and higher-pressure inlet ports to thegovernor-controlled valve, operable to -regulate uid supply to thelatter from the redirection to coarsen the pitch and in the oppositedirection to reduce the pitch, a conduit connected to each end oi saidfluid motor, and means sepagate 4i'ron'i the airscrew to control uidflow through said conduits,sald control means including a casing havingtwo ports communicating with the respective conduits, and having abranched inlet for low pressure fluid, an inlet tor high pressure fluid,and a drain connection, a booster pump receiving oil from one branch ofthe low pressure inlet and arranged to deliver iluid at intermediatepressure within the casing, the casing having adjoining ports arrangedfor communication. respectively, with the second low pressure branch andwith the intermediate pressure source, a valve yconnected todrain andcooperating with said ports to ailord communication alternativelybetween either such pressure port and one or the other conduit, whilstconnecting the other. conduit-to drain. governor-con- -trolled meansoperable to shift said valve to compensate automaticallyv for overspeedor underspeed of the airscrew, a feathering valve in said casing biasedto close of! communication normally between the high pressure inlet andthe intermediate and low pressure ports. and hence to the iiuid motor,and in such position being interposed in the ilow passages between thelow pressure munication when shifted, means to supply the A andintermediate pressure sources and the corresponding casing portsbut saidfeathering valve otherl casing pressure port and a correspondingconduit, while connecting the other to drain, for feathering orunfeathering under the influence of high pressure.

Y ,7. In combination with a variable-pitch propeller having apitch-changing ram operable throughl a normal range of pitch-increaseandJ decrease, and through an abnormal ieathering and unieatheringlrange. of said propeller beyond such normal range of pitch-change, alow-pressure iluid source connected for communication with the ramfor`operation thereof within such normal range. a boosted-pressure fluidsource connected likewise for communication with the ram for op erationwithin such abnormal range, valve means interposed between said ram andthe respective pressure sources, and having four ports and a jdrainoutlet, of which ports one vconnects to the pitch-increasing end of theram and another to its lpitch-decreasing end, a third connects to thelow-pressure source. said ports being arranged in predetermined spacedrelationship, and the `fourth to the boosted-pressure source, agovernorcontrolledwalve member operatively associated withsa'i'pOrtS,and having a plurality of spaced lands arranged, relative to said ports,to connect the low-pressure supply DOrt with the pitch-decreasing end ofthe ram, and the opposite end of the ram to the drain outlet, by-movementof said element in one direction relative to said ports, uponlowered speed, and to connect the boostedpressure supply port with thepitch-increasing end of the ram, and the latters opposite end to l 9 thedrain outlet, by movement of said element in a diilerent directionrelative to said ports, upon increased speed.

8. Control means for use in a hydro-controllable variable-pitchpropeller control system such as vhas a pitch-changing ram operablethrough a normal range of pitch-change under the iniluence of alow-pressure differential between a low-pressure iluid source and adrain, as applied to the opposite ends of said ram, and Aalso operablethrough an abnormal range beyond such normal range under the influenceof a boosted-pressure diierential between a boosted-pressure source andsuch drain, as applied similarly to the opposite ends of said ram; saidcontrol means comprising a casing having a drain outlet and four portsarranged in predetermined spaced relationship for connection, one to thepitchincreasing end of the ram, another to the pitch-decreasing endthereof, a third to the low-pressure source, and the fourth to thevboosted-pressure source; a governor-controlled valve means receivedwithin said casing, movable relative to said ports, said valve meansbeing constructed and arranged in said casing to connect thelow-pressure supply port with that port which connects with thepitch-decreasing end of the ram, and to connect tothe drain outlet thatport which connects with the opposite end of the ram by speed-actuatedmovement of said valve means in said casing in one direction, uponlowered spe'ed, and to connect the boosted-pressure supply port withthat port which connects with the pitch-increasing end of the ram, byspeed-actuated movement of said valve means in said casing in theopposite direction, and to connect to the drain outlet that port whichconnects with the opposite end of the ram,

upon increased speed.

9. In combination with a variable-pitchpropeller having a pitch-changingram operable through a normal range of pitch-increase and decrease,kandthrough an abnormal feathering and unfeathering range of said propellerbeyond such normal range, a low-pressure iluid source, aboosted-pressure fluid` source, and a high-pressure fluid source, acasing having a drain outlet and four ports arranged therein inpredetermined spaced relationship, of which ports one connects to thepitch-increasing end of the ram and another to its pitch-decreasing end,a feathering valve organized and arranged to control admission by Way ofthe third and fourth ports, and

v, normally biased to eiect connection between the low-pressure sourceand the third port, and between the boosted-pressure source and thefourth port, valve means cooperating with said casing ports, speedresponsive means operatively connected to said Valve means to effectmovement thereof in one direction upon lowered speed to connect thelow-pressure source with the pitchdecreasing end of the ram and theopposite end of the ram to drain, and conversely, in the oppositedirection, to connect the boosted-pressure source with thepitch-increasing end of the ram and the opposite end of the ram to thedrain outlet, upon increased speed, means to supply highpressure fluidfrom the corresponding source to said feathering valve, to shift thelatter, and

'thereby to cut off communication between the as has a pitch-changingram operable through a normal range of pitch-decrease under the inuenceof a low-pressure differential as between a low-pressure fluid sourceand a drain, as applied to'opposite ends of such ram, and through a likerange of pitch-increase under the influence of a higher-pressuredierential as between a boostedpressure fluid source and a drain, asapplied similarly to opposite ends of such ram, and through an abnormalfeathering and unfeathering range of said propeller beyond such normalrange under the influence of a high-pressure differential as between ahigh-pressure source and a lower pressure in such ram; said controlmeans comprising a casing having a drain outlet and four portsarrangedtherein in predetermined spaced relationship, for connection,one to the pitch-increasing end of the ram, another to thepitch-decreasing end of the ram, a third normally to the low-pressuresource, and the fourth normally to the boosted-pressure source, afeathering valve arranged for direct connection to the high-pressuresource, and interposed in advance of the ports of said casing betweenthe boosted-pressure and low-pressure sources and the correspondingcasing ports, said feathering valve being biased to normally maintainopen the latter two connections, but upon subjection to thehigh-pressure source being shiftable to cut off communication -betweenthe low-pressure and boosted-pressure sources and saidcasing ports, andto establish communication between said ports and the highpressure iluidconnection, valve means in said casing and cooperating with the severalcasing ports and drain outlets, governor means operatively connected tosaid valve means for movement thereof in one direction upon loweredspeed to connect the low-pressure port with that port which is connectedto the pitch-decreasing end of the ram, and the port which is connectedto the opposite end of the ram to drain, and conversely, in the oppositedirection, to connect the boosted-pressure port with that port which isconnected to the pitch-increasing end of the ram, and the port which isconnected to the opposite end of the ram to drain, upon increased speed,and manual means to shift said governor-controlled valve independentlyof governor action for operations within the feathering range.

11. Control means for use in a variable-pitch airscrew control systemsuch as incorporates a pitch-changing hydro-controllable ram shiftablethrough a normal range of coarsened and reduced pitch, and through anabnormal range, beyond such normal range, for airscrew feathering andunfeathering operations;

- comprising a casing having two ports arranged for connection to therespectively opposite endsv of such ram, and a drain outlet, and havingalso a high pressure inlet, and a branched inlet for lowpressure fluid,the two branches terminating in a normally low-pressure supply port, anda normally intermediate-pressure supply port, respectively, a boosterpump interposed in one branch of said inlet and arranged to deliverfluid at boosted pressure to said intermediate-pressure port, and thesecond branch being connected to said low-pressure port, a valveconnected to drain and cooperating with said ports to affordcommunication alternatively between either such presssure port and oneor the other of the ports connected to the opposite ends of the ram, andto drain the other of such ram-connected ports. governor-controlledmeans operable to shift said valve to compensate automatically foroverspeed said control meansA or underspeed of the airscrew, afeatherlng valve in said casing disposed and biased to close offcommunication normally between the high pressure inlet and theintermediateand low-pressure ports, and hence to the ram, and in suchposition being interposed in the flow passages between the low-pressureinlet and the intermediate-pressure pump and the corresponding casingports, but said feathcring valve being `arranged for communication withthev high-pressure inlet to be shifted under the influence ofhigh-pressure fiuid, when admitted, to cut off communication between thelowand intermediate-pressure branches and the casing ports, and to placethe high-pressure inlet in communication with such ports instead, andindependent valve adjusting means operable to override thegovernor-controlled means by adjustment at will to shift saidgovernor-controlled valve, to afford communication between one or theother casing pressure port and a corresponding ram-connected port,whilst connecting the other ram-connected port to drain, for featheringor unfeathering under the influence of high-pressure fluid automaticallyshifting said feathering valve.

12. .In a controllable-pitch airscrew having blades mounted forpitch-changing movements, a fluid-actuated blade-moving motorhavingopposite fluid-receiving ends, a low-pressure uid source and ahigher pressure fluid source, a sleeve having four axially spaced portsopening into its axial bore, one of said ports communicating with oneend of the blade-moving motor, and an adjacent port communicating withsaid low-pressure source, a third port communicating with the other endof said motor, and the adjacent fourth port communicating with saidhigher-pressure source, a drain outlet, a governor-operated valveslidable in the bore of said sleeve in accordance with airscrew speed,and having axially spaced lands cooperating with said sleeves port,operable to prevent communication between adjacent ports, and furtheroperable upon reciprocation of the valve to establish communicationselectively between one or the other of said motor-connected ports andthat pressure fluid supply port which is adjacent thereto, and betweenthe other of said motor-connected ports and said drain outlet.

13. In combination, a hydraulically controllable variable-pitchpropeller having blades mounted for pitch-changing movements, apitch-changing ram operatively connected to said blades to effect pitchchanges thereof in a range between finepitch and feathering positionsselectively by hydraulically actuated movements of said ram in lonedirection or reversely, a portion of said range including coarse pitchoperating position, a lowpressure uid source connected to supplylowpressure fluid to one end of said ram to effect a decrease in pitchof said blades, an intermediatepressure fluid source connected to supplyintermediate-pressure fluid to the other end of said ram to effect anincrease in pitch of said blades, and a high-pressure fluid sourceconnected to supply high-pressure fluid to the latter end of said ram toeffect feathering vof said blades, and control valve means interposedoperatively in said fluid connections to restrict passage of fluidtherein to said ram from said sources selectively, said valve meansincluding means having a first port opening to the pitch-decreasing endof said ram, a second port opening to the pitch-increasing end of saidram, a third port communicating -a valve passage common to saidintermediate and high pressure sources, opening from said fourth port,said passage branching between said intermediate and high pressuresources, a first valve element normallyclosing the branch communieatingwith said high pressure source and operable automatically in response tohigh-pressure fluid from said high-pressure source to open such branchwhile closing the branch of said passage from said intermediate-pressuresource, and at the same time to interrupt the fluid connection betweensaid low-pressure source and said ram, said high-pressure source beingnormally ineffective to deliver high pressure fluid to said valve means,and a governor actuated valve element coacting with said ports, operableautomatically in response topropeller rotation speed selectively toestablish intercommunication between said rst and third ports whileisolating said second and fourth ports, with a decrease in propellerspeed below a selected value, and to establish intercommunicationbetween said second and fourth ports while isolating saidfirst and thirdports with an increase in propeller speed above a selected value, toregulate speed of said propeller by blade-pitch control thereof betweenfine and coarse pitch under normal operating conditions, whereunder-saidhigh pressure source is ineffective to deliver fluid to said valvemeans, and independent control means connected operatively to saidsecond valve element to effect positioning thereof establishingintercommunication between said second and fourth ports, thereby toenable feathering of said propeller by delivery of high pressure fluidto said valve means and to said ram, said valve means having a fluiddrain passageway therein placed into communication selectively with therespective ends of said r'tm by the control movements of said secondvalve element.

14. The combination as defined inclaim 13 wherein the valve meansincludes a housing structure defining therein a bore operativelyreceiving the second valve element and further defining the four valveports opening into such bore, said ports being arranged in successivespaced relation, the first port lying adjacent to the third port, andthe second port lying adjacent to the fourth port, said second valveelement having -a plurality of lands spaced apart in the direction ofspacing of said ports, and coacting with the bore wall and said ports,movement of which element in such direction selectively establishes andbreaks communication between the adjacent pairs of ports between saidlands, as aforesaid.

15. The combination as dened in claim 13 wherein the valve meansincludes a sleeve element defining therein a cylindrical boreoperatively receiving the second valve element and further dening thefour valve ports formed through the sides of such sleeve, opening intosuch bore, said ports being arranged in successive spaced relation, thefirst port lying adjacent to the third port, the second port lyingadjacent to the fourth port, and the fourth port lying adjacent to thethirdport, said second valve element being tubular and having at leastfour spaced lands coacting with the bore wall and said ports, spacedapart in the direction of spacing of said ports, movement whereof insuch direction selectively establishes and breaks communication betweenthe pairs of ports in two of the spaces between said lands, asaforesaid, and wherein the bore space between lands nearest said rstport com- Y municates with the tubular opening of the tubu- 2,174,717Caldwell et ai. Oct. 3, 1939v Y Name Date Woodward y June 18, 1940 MaderOct. 1, 1940 Caldwell et a1 June 3, 1941 Martin Nov. 25, 1941 Beebe Jan.14,1944

FOREIGN PATENTS (lountryl Date Great Britain Apr. 26, 1938 v GreatBritain Feb. 6, 1940 Great Britain Dec. 15, 1941 Certificate ofCorrection Patent No. 2,461,791. February 15, 1949. ROBERT HENRY WARDEIt is hereby certified that errors appear in the printed speccation ofthe above numbered patent requiring correction as follows:

Column 9, lines 34 to 36, claim 8, strike out the Words and comma byspeedactuated movement of said valve means in said casing in theopposite direction, and insert the same in line 37, after ram,; column11, line 41, claim 12, for port read ports; and that the said LettersPatent should be read With these corrections therein that the sameconform to the record of the case in the Patent Oiice.

Signed and sealed this 2nd day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant 0ommzssz'oner of Patents.

